Bi-directional tapered roller bearing assembly with improved wear resistance

ABSTRACT

The wear resistance of a bi-directional tapered roller bearing is improved by applying a tribological coating to both the small and large end faces of the roller and to at least one of the rib faces of the bearing assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/526,720 filed on Aug. 11, 2009, which is a National Stage ofInternational Application No. PCT/US2008/053947, filed Feb. 14, 2008,which claims priority to U.S. Provisional App. No. 60/892,061, filed onFeb. 28, 2007. The disclosures of which are incorporated herein byreference in their entirety.

FIELD

The present disclosure relates to tapered roller bearings, and inparticular, to a bi-directional tapered roller bearing having improvedwear resistance.

BACKGROUND

Examples of bi-directional tapered roller bearings are shown in U.S.Pat. Nos. 6,464,401 and 5,735,612, which are incorporated herein byreference. Bi-directional bearings handle axial loads in both axialdirections. Such bearings include a cone defining a tapered innerraceway, a cup defining a tapered outer raceway and a plurality oftapered rollers between the inner and outer raceways. The bearingassembly includes at least a thrust rib on the cup adjacent the largediameter end of the roller and a second rib on the cone adjacent thesmall diameter end of the roller. The two ribs have associated ribfaces, and the rollers are positioned between the two rib faces. Incontrast, a uni-directional tapered roller bearing will have only asingle thrust rib.

Bi-directional tapered roller assemblies are susceptible to abrasive andadhesive wear at the sliding contacts between the rolling elements andthe cup/cone rib faces in the presence of debris or in low lubrication(e.g., oil-out) conditions. Experiments have shown that both internallygenerated and external debris are especially harmful at the rib-rollerend contacts because they can become trapped within the multi-ribbearing and cannot easily flow away from the rib/roller end contacts.Similarly, the presence of extra rib-roller end sliding contactsrelative to single rib tapered roller bearing designs can makebi-directional tapered roller bearings more susceptible to rib-rollerend scuffing or scoring damage in oil-out condition.

SUMMARY

A bi-directional tapered roller bearing comprises a tapered innerraceway, a tapered outer raceway facing the tapered inner raceway, and aplurality of tapered rollers positioned between the tapered inner andouter raceways. The tapered rollers have a side surface, a large endface at a large diameter end of the tapered roller and a small end faceat a small diameter end of the tapered roller. The bearing includes atleast a first rib at one of an axial inner or outer edge of the innerraceway and a second rib at the other of the axial inner and outer edgesof the outer raceway. The first and second ribs each define a rib face.One of the rib faces is adjacent the large end of the tapered roller andthe other rib is adjacent the small end of the tapered roller. We havefound that by applying a tribological coating to both the large end andthe small end of the tapered roller the wear resistance of the bearingcan be improved. The coating can also be applied to at least one of thefirst and second rib faces.

The coating can have a thickness of less than 10 μm and a hardness equalto or greater than the hardness of the substrate to which it is applied.The coating can, for example, have a hardness of at least about 9 GPa asmeasured by nanoindentation with a Berkovich diamond indenter.

The coating comprises an amorphous carbon-based or hydrocarbon-basedthin film coating. The coating can be reinforced with titanium (Ti),tungsten (W), chromium (Cr), tantalum (Ta), silicon (Si), vanadium (V),nickel (Ni), niobium (Nb), iron (Fe) or zirconium (Zr) or carbidicinclusions thereof. In a specific embodiment, the coating can comprise atungsten carbide-reinforced amorphous hydrocarbon nano-compositecoating.

The coating comprises an adhesion layer applied to the surface of thesubstrate to be coated and a top functional layer over the adhesionlayer. The adhesion layer can be chromium (Cr), titanium (Ti), tantalum(Ta), nickel (Ni), molybdenum (Mo), iron (Fe) or silicon (Si). Althoughit is preferred that the adhesion layer be comprised of the dominantelement only (e.g., 100 atomic % Cr), it can include other elements suchas carbon (C), hydrogen (H), oxygen (O) and combinations thereof.However, if the adhesion layer includes C, H or O, the C, H and/or Oshall comprise no more than about 75 atomic % of the adhesion layer.That is, the dominant element comprises at least 25 atomic % of theadhesion layer.

The top functional layer can be a hard carbonaceous layer that iscomprised of amorphous carbon or amorphous hydrocarbon. The topfunctional layer can consist only of amorphous carbon (C) or amorphoushydrocarbon (a:C—H). Alternatively, the top functional layer can includethe elements oxygen (O), nitrogen (N), boron (B), fluorine (F) orcombinations thereof. The carbonaceous top layer may also include Ti, W,Cr, Ta, Si, V, Nb, Zr, Mo, O, N, B, F or combinations thereof asadditive elements. However, the additive element(s) shall not exceed 50atomic % of the total top layer composition, the balance of compositionbeing carbon and hydrogen. It is also possible for the carbonaceousfunctional top layer to have no additives and consist of only amorphouscarbon or amorphous hydrocarbon.

In one variation, the coating can include a gradient layer between theadhesion layer and the top functional layer. In this instance, thegradient layer transforms from the composition of the adhesion layeradjacent the adhesion layer to the composition of the top functionallayer adjacent the top functional layer. In another variation, thecoating can include a Cr/WC/a-C:H gradient layer over the adhesion layerand a WC/a-C:H mid-layer over the gradient layer. The top functionallayer covers the mid-layer and is comprised of a-C:H.

DRAWINGS

FIG. 1 is a cross-sectional view of a bi-directional tapered rollerbearing applied to a member;

FIG. 2 is an enlarged fragmentary cross-sectional view of the bearing;and

FIG. 3 is an enlarged schematic drawing of a coating applied to asurface of the bearing.

Corresponding reference numerals will be used throughout the severalfigures of the drawings.

DETAILED DESCRIPTION

The following detailed description illustrates the invention by way ofexample and not by way of limitation. This description will clearlyenable one skilled in the art to make and use the invention, anddescribes several embodiments, adaptations, variations, alternatives anduses of the invention, including what we presently believe is the bestmode of carrying out the invention. Additionally, it is to be understoodthat the invention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or being carried outin various ways. Also, it is to be understood that the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting.

A bi-directional tapered roller bearing 10 is shown generally in FIGS. 1and 2. The bearing 10 comprises a cone 12 defining an inner taperedraceway 14, a cup 16 defining a tapered outer raceway 18, and aplurality of tapered rollers 20 positioned between the inner and outerraceways. The rollers 20 are separated from each other by a cage 22. Therollers 20 each have a large diameter end 20 a, a small diameter end 20b and a tapered surface 20 c. The inner and outer raceways 14 and 18 andthe roller surface 20 c are all formed such that there is rolling motionbetween the rollers and the raceways. The cone 12 includes a thrust rib24 at a wide diameter end of the raceway 14. A rib ring 25 adjacent thesmall diameter end of the raceway 14 defines a retaining rib 26 which isadjacent the small diameter end of the raceway 14. A third rib 28adjacent the cup 16 is positioned to be adjacent the large diameter end22 a of the roller. The retaining rib 26 is separate from the cone 12and the third rib is separate from the cup 16 to facilitate assembly ofthe bearing assembly. The ribs 24, 26 and 28 each define respective ribfaces 24 a, 26 a and 28 a, respectively which are generallyperpendicular to the raceway. The rib 24 is shown to be integral withthe cone 12, while the ribs 26 and 28 are shown to be separate fromtheir respective races. However, the bearing assembly can be made withthe ribs 26 and 28 integral with their races and with the rib 24 beingseparate from its race.

Sliding contact occurs between the large and small ends of the rollersand the rib faces. Hence, in the bearing 10, sliding contact will occurbetween the roller large end 20 a and the rib faces 24 a and 28 a aswell as between the roller small end 20 b and the rib face 26 a.Experiments have shown that both internally-generated and externaldebris are especially harmful at the rib-roller end contact because thedebris can become trapped within the multi-rib bearing assembly, andcannot easily flow away from the rib/roller interface. Further, thepresence of the extra rib/roller interfaces (as compared touni-directional thrust tapered roller bearings which have only a singlethrust rib) makes bi-directional roller bearings more susceptible torib-roller end scuffing or scoring damage in oil-out conditions.

If a bi-directional tapered roller bearing experiences failure, thedebris generated from the raceways cannot escape the contact regions.This leads to severe adhesive wear at the sliding rib-roller endcontacts, ultimately resulting in excessive bearing torque (andfailure). Application testing with coatings on only the roller ends 20a,b protected the roller end surfaces, but did not prevent massiveadhesive wear damage on the rib faces that resulted from debrisparticle/rib face adhesive interactions in the sliding contacts. Coatingat least one rib face in addition to the roller ends is expected todelay debris-related failure of the rib and thus improve the overallwear resistance of the bearing.

The coating is an amorphous carbon or hydrocarbon (sometimes referred toas a diamond-like carbon, or DLC) based thin film tribological coating.As just noted, the coating is applied to the roller end faces andoptionally to one or both of the rib faces. Preferably, the coating isapplied to the end faces of all the rollers in the bearing assembly. Oneacceptable coating is a WC/aC:H coating available from The TimkenCompany under the name ES300. The coating has a thickness of less thanabout 10 micrometers. The coating has a hardness equal to or greaterthan the hardness of the substrate to which it is applied. The coatingcan, for example, have a hardness of at least about 9 GPa as measured bynanoindentation with a Berkovich diamond indenter. The DLC coating canbe reinforced with additional elements such as titanium (Ti), tungsten(W), chromium (Cr), tantalum (Ta), silicon (Si), vanadium (V), nickel(Ni), niobium (Nb), iron (Fe) or zirconium (Zr) or carbidic inclusionsthereof. In one illustrative embodiment, the coating is a tungstencarbide-reinforced amorphous hydrocarbon nano-composite coating. Thetungsten carbide-reinforced amorphous hydrocarbon nano-composite coatingis a member of this class.

The coating C (FIG. 3) comprises at least two layers, an adhesive layeror interlayer 40 which is applied to the substrate S (i.e., rib face orroller end) and a top functional layer 42 which covers the adhesionlayer 40. The adhesion layer can be chromium (Cr), titanium (Ti),tantalum (Ta), nickel (Ni), molybdenum (Mo), iron (Fe) or silicon (Si).Although it is preferred that the adhesion layer 40 be comprised of thedominant element only (e.g., 100 atomic % Cr), it can include otherelements such as carbon (C), hydrogen (H), oxygen (O) and combinationsthereof. However, the C, H and/or O shall comprise no more than about 75atomic % of the adhesion layer. Stated differently, the dominant elementcomprises at least 25 atomic % of the adhesion layer.

The top functional layer 42 comprises amorphous carbon (or amorphoushydrocarbon). The top functional layer may include the elements oxygen(O), nitrogen (N), boron (B), fluorine (F) or combinations thereof. Thecarbonaceous top layer may include one or more of the additive elementsnoted above (Ti, W, Cr, Ta, Si, V, Nb, Zr, Mo, O, N, B, and F). However,the amount of additive element(s) shall not exceed 50 atomic % of thetotal top layer composition, the balance of the top layer compositionbeing carbon and hydrogen. It is also possible for the carbonaceousfunctional top layer to have no additives and consist of only amorphouscarbon (C) or amorphous hydrocarbon (C and H).

Typically, for a steel substrate, the adhesion layer 40 will be chromium(Cr) and the functional layer 42 will be a hard carbonaceous layer. Agradient layer 44 can be formed between the adhesion layer 40 and thetop functional layer 42 with the gradient layer transforming from thecomposition of the adhesion layer to the composition of the final or topfunctional layer. Coatings with additional layers are also included,such as Cr (adhesion layer)+Cr/WC/a-C:H (gradient layer)+WC/a-C:H(mid-layer)+a-C:H (top layer). In this instance, the gradient layer willtransform from being chromium adjacent the adhesive layer to beingWC/a-C:H. The WC/a-C:H mid-layer will then transform from being WC/a-C:Hadjacent the gradient layer to being a-C:H adjacent the top functionallayer. Hence, the mid-layer defines a second gradient layer. It isimportant that the top functional layer be a hard carbonaceous layer inany embodiment of the coating (which may or may not include the otherelements as described above).

The coating composition that is applied to the roller end faces and therib faces need not be the same. For example, the a WC/a-C:H coating canbe applied to the roller ends and a TiC/a-C:H coating can be applied tothe rib faces.

The coating can be deposited using plasma techniques for vapordeposition, but is not limited to physical vapor deposition (PVD) orplasma-enhanced chemical vapor deposition (PECVD). As is known, thegradient layers are formed by changing the ratio of components that arebeing coated onto the substrate. Thus, there is no sharp line separationbetween adjacent layers.

We expect that by applying a wear resistant coating to both the smalland large ends of all the rollers and optionally to at least one ribface will improve the wear resistance of the bearing assembly.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. A bi-directional tapered roller bearing comprising a tapered innerraceway, a tapered outer raceway facing the tapered inner raceway, and aplurality of tapered rollers positioned between the tapered inner andouter raceways; the tapered rollers having a side surface, a large endface at a large diameter end of the tapered roller and a small end faceat a small diameter end of the tapered roller; the bearing including afirst rib at one of an axial inner or outer edge of said inner racewayand a second rib at the other of the axial inner and outer edges of saidouter raceway, said first and second ribs each defining a rib face; oneof said rib faces being adjacent the large end of said tapered rollerand the other rib being adjacent the small end of the tapered roller;the bearing further including a tribological coating applied to both thelarge end and the small end of the tapered roller and to at least one ofthe first and second rib faces; the coating being an amorphouscarbon-based or hydrocarbon-based thin film coating.
 2. The bearing ofclaim 1 wherein the tribological coating is on both said first rib faceand said second rib face.
 3. The bearing of claim 1 wherein said coatinghas a thickness of less than 10 μm.
 4. The bearing of claim 1 whereinsaid coating has a hardness equal to or greater than the hardness of thesubstrate to which it is applied.
 5. The bearing of claim 4 wherein thecoating has a hardness of at least about 9 GPa as measured bynanoindentation with a Berkovich diamond indenter.
 6. The bearing ofclaim 1 wherein the coating comprises an adhesion layer applied to thesurface to be coated and a top functional layer about the adhesionlayer; the functional layer being a hard carbonaceous layer.
 7. Thebearing of claim 6 wherein the adhesion layer is chosen from the groupconsisting of chromium (Cr), titanium (Ti), tantalum (Ta), nickel (Ni),molybdenum (Mo), iron (Fe) or silicon (Si); the adhesion layer as pureas possible in the dominant element.
 8. The bearing of claim 6 whereinone or more additives are present in the carbonaceous top layer; theadditives being chosen from the group consisting of chromium (Cr),titanium (Ti), tantalum (Ta), nickel (Ni), molybdenum (Mo), iron (Fe),silicon (Si), tungsten (W), vanadium (V), niobium (Nb), zirconium (Zr),oxygen (O), nitrogen (N), boron (B), fluoride (F), carbidic inclusionsand combinations thereof; the additives comprising 50 atomic % or lessof the total top layer composition, the balance of top layer compositionbeing carbon and hydrogen.
 9. The bearing of claim 6 wherein thecarbonaceous functional top layer has no additives and consists of onlyamorphous carbon (C) or hydrocarbon (C and H).
 10. A bi-directionaltapered roller bearing comprising: a tapered inner raceway; a taperedouter raceway facing the tapered inner raceway; a plurality of taperedrollers positioned between the tapered inner raceway and the taperedouter raceway, the tapered rollers having a side surface, a large endface at a large diameter end of the tapered roller and a small end faceat a small diameter end of the tapered roller; a first rib at an axialouter edge of the inner raceway; a second rib at an axial inner edge ofthe inner raceway; a third rib at an axial outer edge of the outerraceway, the first rib, the second rib and the third rib respectivelydefine a first rib face, a second rib face and a third rib face, thefirst and third rib faces being adjacent the large end of the taperedroller and the second rib face being adjacent the small end of thetapered roller; and a tribological coating applied to both the large endand the small end of the tapered roller and to one or more of the firstrib face, the second rib face and the third rib face, the coating beingan amorphous carbon-based or hydrocarbon-based thin film coating that isnon-adhesive to metallic debris particles within the bearing such thatthe coating prevents wear of the roller ends and the respective one ormore of the first rib face, the second rib face and the third rib facecaused by the metallic debris particles.
 11. The bearing of claim 10wherein the tribological coating is on both said first rib face and saidsecond rib face.
 12. The bearing of claim 10 wherein said coating has athickness of less than 10 μm.
 13. The bearing of claim 10 wherein saidcoating has a hardness equal to or greater than the hardness of asubstrate to which it is applied.
 14. The bearing of claim 13 whereinthe coating has a hardness of at least about 9 GPa as measured bynanoindentation with a Berkovich diamond indenter.
 15. The bearing ofclaim 10 wherein the coating comprises an adhesion layer applied to thesurface to be coated and a top functional layer over the adhesion layer;the functional layer being a carbonaceous layer.
 16. The bearing ofclaim 15 wherein the adhesion layer is chosen from the group consistingof chromium (Cr), titanium (Ti), tantalum (Ta), nickel (Ni), molybdenum(Mo), iron (Fe) or silicon (Si).
 17. The bearing of claim 15 wherein theadhesion layer includes low levels carbon (C), hydrogen (H), oxygen (O)and combinations thereof, the amount of C, H and/or O in the adhesionlayer not exceeding about 75 atomic % of the adhesion layer.
 18. Thebearing of claim 15 wherein one or more additives are present in thecarbonaceous top layer; the additives being chosen from the groupconsisting of chromium (Cr), titanium (Ti), tantalum (Ta), nickel (Ni),molybdenum (Mo), iron (Fe), silicon (Si), tungsten (W), vanadium (V),niobium (Nb), zirconium (Zr), oxygen (O), nitrogen (N), boron (B),fluoride (F), carbidic inclusions and combinations thereof; theadditives comprising 50 atomic % or less of the total top layercomposition, the balance of top layer composition being carbon andhydrogen.
 19. The bearing of claim 15 wherein the carbonaceousfunctional top layer has no additives and consists of only amorphouscarbon (C) or hydrocarbon (C and H).
 20. The bearing of claim 15 whereinthe coating includes a gradient layer between the adhesion layer and thetop functional layer, the gradient layer transforming from thecomposition of the adhesion layer to the composition of the final layer.